Debugging warning messages

I’m getting a lot of the following in the logs. How do I begin to debug
this?

[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Use of uninitialized value in string eq at
/usr/local/share/perl5/HTML/FormatText/WithLinks.pm line 143.
(/usr/local/share/perl5/HTML/FormatText/WithLinks.pm:143)
[warning]: Deep recursion on subroutine “HTML::Element::delete” at
/usr/local/share/perl5/HTML/Element.pm line 567.
(/usr/local/share/perl5/HTML/Element.pm:567)
[warning]: Deep recursion on subroutine “HTML::Element::delete_content” at
/usr/local/share/perl5/HTML/Element.pm line 580.
(/usr/local/share/perl5/HTML/Element.pm:580)
[warning]: Deep recursion on subroutine “HTML::Element::delete” at
/usr/local/share/perl5/HTML/Element.pm line 567.
(/usr/local/share/perl5/HTML/Element.pm:567)
[warning]: Deep recursion on subroutine “HTML::Element::delete_content” at
/usr/local/share/perl5/HTML/Element.pm line 580.
(/usr/local/share/perl5/HTML/Element.pm:580)